Cobalt base alloy



United States Patent 3,418,111 COBALT BASE ALLOY Robert B. Herchenroeder, Kokomo, Ind., assignor to Union Carbide Corporation, a corporation of New ork No Drawing. Filed Oct. 27, 1966, Ser. No. 589,822 3 Claims. (Cl. 75171) This invention relates to cobalt base alloys. More particularly, this invention relates to cobalt-chromiumtungsten-nickel alloys containing relatively small amounts of lanthanum which are characterized by improved oxidation resistance at high temperatures in addition to having excellent high temperature mechanical properties.

Cobalt base alloys have been used extensively in the past for high temperature applications and have been found to be generally satisfactory except that in some instances they have been lacking in oxidation resistance, when compared to nickel base alloys. However, at high temperatures, on the order of 1800 to 2100 F. nickel base alloys have limited mechanical properties. Accordingly, it would represent an advance in the art if cobalt base alloys could be provided with oxidation resistance comparable to or better than that of nickel base alloys at high temperatures, while retaining the characteristic strength and mechanical properties of cobalt base alloys at high temperatures.

It is therefore an object of the present invention to provide a cobalt base alloy having improved oxidation resistance at elevated temperatures.

It is another object of the present invention to provide a cobalt base alloy having excellent high temperature mechanical properties and additionally having improved oxidation resistance.

Other objects will be apparent from the following description and claims.

A cobalt base alloy in accordance with the present invention is an alloy consisting essentially of about Percent Chromium 18-30 Tungsten 8-18 Iron Up to 10 Carbon 0.01-0.35 Nickel 8-30 Silicon Up to l Lathanum 0.02-0.2

Cobalt, balance to 61% maximum.

wherein the percent Cr-i-percent W percent C ratio in the alloy is at least about 110, with an alloy having a ratio of less than about 200 containing at least about 0.2% silicon.

A preferred range of the alloy of the present invention is as follows:

Cobalt, balance to 61% maximum.

Alloys in the foregoing range have been found to have an optimum combination of oxidation resistance and mechanical properties at high temperatures.

"ice

In addition to the specifically mentioned alloy constituents, other metals can be adventitiously present in the all'oy of this invetnion in minor amounts. For example, zirconium may be present in amounts up to about 2%; vanadium up to about 2%; up to about 1% berylium; boron up to about 0.02%; manganese up to about 2%; Ti-i-Al up to about 4%; Ta+Cb up to about 8%.

It has been discovered, as part of the present invention that with alloy compositions as described above, a relatively small lanthanum addition provides remarkable oxidation resistance at high temperatures when the critical and defined relationship between chromium, tungsten, carbon and silicon is observed.

It has also been discovered that other rare earth metals can be present with the lanthanum, such as occurs when mischmetal is used to introduce lanthanum, without detrimentally effecting the improved oxidation resistance. However, the presence of other rare earth metals, in an aggregate amount exceeding the lanthanum content, results in the formation of stringers and non-metallic inclusions in the alloy which adversely affect its weldability and result in low strength welds. Consequently, for alloys intended for welding applications, the lanthanum is preferably added in esentially elemental form, and should, in any event, exceed the aggregate amount of other rare earth metals in the final alloy. For alloys which are not intended for welding, however, the lanthanum addition can be made using any convenient technique such as mischmetal, elemental lanthanum or lanthanum containing alloys.

Table I shows alloy compositions which have been prepared by being melted, cast into ingots of about 20-25 lbs., forged to plate about to /4, inch thick, hot rolled to sheet and annealed at 2100-2250 F. for 10-15 minutes and quenched. The lanthanum additions to alloys K and L were made in the form of mischmetal and for the other lanthanum-containing alloys the addition was made using either elemental lanthanum or lanthanum-cobalt alloy containing about 20% lanthanum.

Specimens of the various alloys of Table I, in sheet form inch x inch x 0.06-0.125 inch thick, were tested for oxidation resistance and the results are shown in Table II.

The procedure for the oxidation tests to which the alloy specimens were subjected was as follows:

One hundred hour continuous oxidation test.

(1)Prepare specimen by grinding all surfaces to a 120 grit finish.

(2) Measure the surface area of specimen and weight.

(3) Expose the specimen at 2000" F. continuously for hours in dry flowing air (2 cubic feet per hour).

(4) Air cool the sample.

(5 Descale the sample in a salt bath.

(6) Carefully weigh the descaled sample and calculate the Weight loss.

(7) Calculating the depth of penetration per year of exposure follows:

Weight loss 1 density 100 hours area of sample hours/year TABLE I W Fe Ni Mn B Si Al La Co 12. 68 2. 0.10 19.40 0. 56 0. 005 0. 01 0. 08 0. 04 B31. 14. 02 2. 43 0.12 19.48 0. 64 0. 015 0. 03 0. 28 0. 05 B31. 14.64 2. 01 0. 09 10. 41 1.30 0. 003 0.14 0. 13 381. 12. 28 2. 38 0. 29 19. 0. 72 0. 013 0. 32 0. 09 Bal. 14. 75 1. 43 0. 09 18.80 0. 66 0.016 0.11 0.18 0.12 B81. 14. 48 1.88 0. 11 25. 0. 54 0. 012 0. 01 0. 18 0. 08 1331. 14.81 1. 30 0. 09 18. 88 0. 56 0.018 0.1 0. 20 0. 13 Bal. 14.55 1.18 0.11 18.88 0. 56 0.016 0. 19 0.18 0.10 B31. 17. 66 1. 38 0.12 23.16 0. 67 0. 021 0. 17 0. 28 0. 04 B81. 14.88 1. 23 0.10 19.32 0. 56 0. 018 0. 21 0. 30 0. 04 B31. 12. 62 2. 0. 10 18. 44 0. 44 0. 005 0. 03 0. 13 0. 02 1331. 12.62 2. 35 0.10 18.44 0. 44 0. 005 0. 03 0. 13 0. 04 Bal. 14.47 1. 35 0.10 19. 20 0. 64 0. 013 0. 06 0.15 0. 06 Bal. 14. 2. 48 0. 08 19.24 1. 10 0. 016 0. 03 0. 21 0. 08 Bal. 14.39 3. 30 0. 07 19. 08 1. 06 0. 016 0. 05 0. 18 0. 05 Bal. 14.38 3. 25 0. 06 18.88 1.90 0. 016 0. 04 0.13 0. 04 B81. 12.35 2. 58 0. 12 19.60 0. 88 0. 001 0. 64 0. 23 0. 06 B31. 13. 42 1. 65 0. 11 20. 76 0. 42 0.001 0. 31 0. 03 Ba]. 13.43 1.43 0.13 21.80 0.36 0.003 0.26 0 33 0.06 B81. 12.68 2.15 0.10 19.40 0.56 0.005 0.01 0.08 1321. 13.00 1.68 0.30 19.20 0.64 0.018 0. 08 Bal. 13.00 1. 68 0. 29 19. 20 0. 64 0.018 0. 08 0. O8 0. 05 B81. 14.02 2.43 0.11 19.43 0.64 0.015 0. 08 0.28 1331. 14.84 1.85 0.10 10.40 1.46 0. 009 0.05 0. 05 B31.

1 0.47 Mo. 3 Total rare earth content=0.08%. 3 Total rare earth content -0.34%.

TABLE II OXIDATION RATE IN MILS PER YEAR tiOnS and is a particularly PI'CfeI'I'ed Of the present invention. AHOY 5.33? 25 As shown by the test data of Table III, alloys of this 20 33 invention, in addition to having improved oxidation resist- 20 ance, are also characterized by excellent mechanical prop- 2 $2 erties at high temperatures. It can also be seen from 7 14 0 Table III that the alloys of the present invention, which 13 8 3 exhibited oxidation resistance com arable to Hastello Al- 10 23 f 12 19 loy X, have much better mechanical properties particu- 3 g larly at higher temperatures. 13 14 9 12 TABLE III 22 9 35 12 13 0.2% offset Ultimate Elongation, 17 19 yield strength, tensile strength, percent 14 14 Alloy K p.s.1. K p.s.i. 11 10 14 15 1,600 F. 2,000 F. 1.600 F. 2,000 F. 1,600 F. 2,000 F.

7 7 23 39 51 179 25 283 23 47 X 31 143 Hastelloy alloy X 21 As can be seen from Table II, alloys A through S, which contain lanthanum and are within the scope of the present invention, have superior oxidation properties as compared to alloys T through X, which while generally similar in composition, are outside of the compositional limits of this invention. Alloys T, U, W and X, for ex- Hastelloy ample, do not contain lanthanum and can be seen to be a loy X- -7 8- 6-5 0 considerably less oxidation resistant, particularly under intermittent conditions, then alloys in the group A through What is claimed is:

S of similar composition but which additionally contain a 1 An alloy characterized by improved resistance to lanthanum addition- AHOY While containing lanthanum dation at elevated temperatures consisting essentially in does not have a suificiently high 55 Weight cent of about;

0 W iPercent Chrominum 18-30 Tungsten 8-18 ratio, and is characterized by very poor oxidation resist- Iron Up to 10 anee under intermittent conditions. Carbon 0 01 3 5 Hastelloy Alloy X a widely used nickel base alloy Nickel (nominal composition: 22% Cr, 1% W, 9% Mo, 18% Fe, Silicon Up to 1 0.1% C, 2.5% max. Co, Ni bal.), generally considered Lanthanum 0.02 0 2 to be the industry standard for oxidation resistance, was

also tested under intermittent conditions and the result Cobalt balance to 61% maxlmum' recorded in Table II to show the significance of the imwherein the proved oxidation resistant properties of the cobalt base alloys of this invention.

Alloy 8 (AIM composition: 21-22% Cr, 13-14% W, percent C +p W 12% Fe, 22% Ni, 0.3% Si, 0.1% C, 0.06% La, balance percent C Co) can be seen from Table II to have exceptional oxidation resistance under continuous and intermittent condiratio in the alloy is at least about 10 i an n 1 wk 9f union Carbide Corporation 7 rzitliirggiless than about 200 containing at least about 2. An alloy in accordance with claim 1 consisting essentially of about:

Percent Chromium 19-28 Tungsten 12-18 Iron Up to 5 Carbon 0.01-0.15

Nickel 10-25 Silicon Up to 0.6 Lanthanum 0.02-0.15

Cobalt, balance to 61% maximum.

Iron 1-2 Carbon 0.1

Nickel 22 Silicon 0.3 Lanthanum 0.06 Cobalt Balance References Cited UNITED STATES PATENTS 2,075,718 3/1937 Hessenbruch 75-17l 2,744,010 5/1956 Callaway 75-171 2,746,860 5/1956 Binder et al. 75171 3,304,176 2/1967 Wlodek 75-171 3,366,478 1/1968 Wheaten 75--171 RICHARD O. DEAN, Primary Examiner. 

